122 4VIr Babbage on the Theoretical Principles 
of changes have taken place in succession, giving to the earth its 
present character, and fitting it for the residence of its present 
inhabitants. And if the same system of change pontinues to 
operate (and it must do so while gravitation prevails), the earth 
may become an unfit dwelling for the present tribes, and revolu- 
tions may take place, as extensive as those which living beings 
have already experienced. 
In addition to these circumstances, which must have exercised 
a powerful influence on the distribution of animals, we must bear 
in mind, that the universal deluge of Noah, and the numerous 
local inundations, the traces of which may be perceived in every 
country, must have greatly contributed to produce changes in 
the animal and vegetable kingdom. To these inundations may 
be ascribed the occurrence of the remains of supposed land 
plants, and fresh-water animals in strata, alternating with such 
as contain only marine exuviae. These appearances occur in the 
secondary formations of all ages. 
Art. NX. — On the Theoretical Principles of the Machinery 
for Calculating Tables *. In a Letter from Charles Bab- 
bage, Esq. E. R. S. Lond. & Edin. to Dr Brewster. 
My Dear Sir, 
HaVING, during the last two or three months, laid aside the 
further construction of machinery for calculating tables, I have 
occasionally employed myself in examining the theoretical prin- 
ciples on which it is founded. Several singular results having 
presented themselves in these inquiries, I am induced to com- 
municate some of them to you, less from the importance of the 
analytical difficulties they present, than from the curious fact 
which they offer in the history of invention. 
I had mentioned to you, that, before I left London, I had 
completed a small engine, which calculated tables by means of 
differences. On considering this machine, a new arrangement 
occurred to me, by which an engine might be constructed, that 
See this Journal , Vol. VII. p. 271. 
